When an impact from a backside is applied to a vehicle in a condition where an occupant is not leaned on a seatback, a head of the occupant rapidly moves toward a headrest with a rapid movement of an upper body of the occupant toward the seatback. On this occasion, a moving distance of the upper body of the occupant differs from a moving distance of the head of the occupant. More specifically, the head of the occupant moves further toward the backside of the vehicle than the upper body of the occupant. Then, the upper body of the occupant is swung by a large amount forward on the rebound of the impact. At this time, a neck of the occupant is strained because of a difference between the moving distance of the upper body and the head.
A headrest apparatus, which moves the headrest to a position of the head of the occupant when the impact from the backside is applied to the vehicle, is respectively disclosed in JP2000-211410A and JP2003-54343A. With such configuration, the head of the occupant is prevented from being moved by a large amount backward and is protected in a condition where the impact from the backside is applied to the vehicle. Accordingly, a burden to the neck of the occupant can be reduced.
According to the headrest apparatuses disclosed in JP2000211410A and JP200354343A, the head of the occupant is protected by temporally stopping the headrest after moving the headrest to the position of the head of the occupant. A time required for protecting the head of the occupant by the headrest depends on an impact speed, an impact force applied to the vehicle, a posture of the occupant, or the like. Therefore, the head of the occupant can reliably be protected when the time for protecting the head of the occupant is set longer. However, in such a condition, the headrest, which is protruded forward, may hinder a driving ability of the occupant whose head has already been protected.
The present invention has been made in view of the above circumstances, and provides a headrest apparatus which protects a head of an occupant without hindering a driving ability of the occupant because of a front portion of a headrest.